Hi,
This is not a well-known amplifier, so here is a review I wrote years ago about it:
http://www.musicgearreview.com/reviews.php?man=Montarbo&cat=Guitar_Amplifiers&mod=165%20NR
And Schematics I had directly from the company:

Greetings (and happy new year),
I'm new to this forum, this is my first post.
I have a Montarbo guitar amp that I really like. It was made in Italy in the 70s, and is solid state.
Here is my problem / question:
I now live in the US, and, as the amp is original, it is designed for the 230V/50Hz electric system. I've used it with success through a converter (which by the way converts voltage but doesn't change the 60Hz frequency). Problem: this is not very convenient, and it generates quite an amount of noise.
Sorry if the question sounds dumb (I'm in the newbie section, right?), but is there any risk in using the amp directly on the US 120V system (with the proper plug adapter)? My poor knowledge of electronics makes me think it might loose power, which is not really an issue, but would it explode in my face? be damaged? sound dull? I wouldn't ask the question if I was interested in doing things the other way (plugging a US amp on European system) as I assume some electronic components might not appreciate the voltage difference.
Thanks!

PS: I think I have some schematics somewhere of this amp, if that can help